/Engine/Plugins/Editor/UVEditor/Source/UVEditorTools/Public/Selection/UVToolSelectionHighlightMechanic.h
When true, edge selections also highlight the edge pairings (i.e. edges that could weld with the selected edges). Note that the call itself controls visibility and the next rebuild call, but won't cause an immediate rebuild on its own.
void SetEnablePairedEdgeHighlights ( bool bEnable )